Airfoils are well known in the prior art. Aircraft wings, propellers and rotors are well known examples of airfoils. An aircraft wing achieves lift by causing the air that flows above it to travel at a higher rate of speed than the air passing underneath it. In accordance with Bernoulli's Principle, the air traveling at a higher rate of speed above the wing is at a lower pressure than the air under the wing. The result is an upwardly directed lifting force.
As a result of the higher air pressure under the wing, air vortices tend to form at the outboard tip. The reason the vortices are formed is explained with reference to FIG. 1. FIG. 1 shows a back view of a wing or other airfoil 10. As air flows past the wing, an area of relatively high pressure 12 is created below the wing. An area of relatively lower pressure 14 is created above the wing. At the outboard tip 16 air tends to spill over the tip from the higher pressure area 12 to the lower pressure area 14. When this occurs, the air tends to move in a rotational direction as indicated by Arrow V. This rotational movement of the air causes a vortex to form which extends a distance behind the moving airfoil.
The vortices that occur at the tips of airfoils have several drawbacks. First, the vortices consume energy that would otherwise be used to move the aircraft. As a result, the creation of a vortex increases drag. This drag is significant because the tangential velocity of a vortex on a wing may be as high as 70 percent of the free stream velocity of the air passing over the wing. This high velocity in the vortex consumes considerable energy.
A further drawback associated with wing tip vortices in aircraft is that the vortices extend a considerable distance behind the plane. As a result, the vortices pose hazards for following aircraft. This may result in the need to space the aircraft greater distances, particularly during takeoff and landing.
Efforts have been made in the past to attenuate the effect of airfoil tip vortices. U.S. Pat. No. 3,411,738 discloses an airfoil with outboard extensions designed to minimize the spillage of air over the wings. This design, which has "gull wing" type extensions that extend downwardly and outwardly from the ends of the wing, holds more of the air under the wing and attempts to direct the vortex downwardly away from the aircraft.
I previously developed a vortex generator for an airfoil which is shown in U.S. Pat. No. 3,596,854. My vortex generator operates to concentrate the vortex at the outboard tip of an airfoil and thereby minimize the scope of its deleterious effects.
None of the approaches known in the prior art minimize the problem of vortices to a desirable degree. Thus, there exists a need for an airfoil that attenuates the vortices at the outboard tip.